/**
 * 本程序主要用于对参数产生格式化的输出
 */
#include <stdarg.h>
#include <string.h>

#define is_digit(c)	((c) >= '0' && (c) <= '9')

static int skip_atoi(const char **s) {
	int i = 0;

	while (is_digit(**s))
		i = i * 10 + *((*s)++) - '0';
	return i;
}

#define ZEROPAD	1		/* pad with zero */
#define SIGN	2		/* unsigned/signed long */
#define PLUS	4		/* show plus */
#define SPACE	8		/* space if plus */
#define LEFT	16		/* left justified */
#define SPECIAL	32		/* 0x */
#define SMALL	64		/* use 'abcdef' instead of 'ABCDEF' */

//大括号表达式集合，值为最后一个表达式
#define do_div(n,base) ({ \
int __res; \
__asm__("divl %4":"=a" (n),"=d" (__res):"0" (n),"1" (0),"r" (base)); \
__res; })

/**
 *将整数转换成指定进制的字符串
 *str：转换后的字符串
 *num:需要转换的整数
 *base:进制
 *size:整数部分长度
 *precision：数字精度
 *type:flag类型
 */
static char * number(char * str, int num, int base, int size, int precision,
		int type) {
	char c, sign, tmp[36];
	int i;
	const char *digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	if (type & SMALL)
		digits = "0123456789abcdefghijklmnopqrstuvwxyz";
	if (type & LEFT)
		type &= ~ZEROPAD; //如果类型为左对齐，则屏蔽填0标志位
	if (base < 2 || base > 36) //不支持的进制
		return 0;
	c = (type & ZEROPAD) ? '0' : ' ';
	if (type & SIGN && num < 0) { //判断标志符为：+，-或' '.
		sign = '-';
		num = -num; //负数
	} else
		sign = (type & PLUS) ? '+' : ((type & SPACE) ? ' ' : 0);
	if (sign)
		size--; //符号不为0
	if (type & SPECIAL) //特殊类型符号
		if (base == 16)
			size -= 2; //0x size-2
		else if (base == 8)
			size--; //0 size-1
	i = 0;
	if (num == 0)
		tmp[i++] = '0';
	else
		while (num != 0)
			tmp[i++] = digits[do_div(num,base)];
	if (i > precision)
		precision = i;
	size -= precision;
	if (!(type & (ZEROPAD + LEFT))) //不是左对齐，且补空格
		while (size-- > 0)
			*str++ = ' ';
	if (sign) //符号
		*str++ = sign;
	if (type & SPECIAL)
		if (base == 8)
			*str++ = '0';
		else if (base == 16) {
			*str++ = '0';
			*str++ = digits[33];
		}
	if (!(type & LEFT))
		while (size-- > 0)
			*str++ = c;
	while (i < precision--)
		*str++ = '0';
	while (i-- > 0)
		*str++ = tmp[i];
	while (size-- > 0)
		*str++ = ' ';
	return str;
}

/**
 * 将字符串格式化后存入buf
 * return 返回字符串长度
 */
int vsprintf(char *buf, const char *fmt, va_list args) {
	int *ip;
	int len;
	int i;
	char *s;
	char *str;
	int flags;
	int field_width;
	int precision;
	int qualifier;
	for (str = buf; *fmt; ++fmt) {
		if (*fmt != '%') {
			*str++ = *fmt;
			continue;
		}
		repeat: flags = 0;
		++fmt; //skip '%'
		switch (*fmt) {
		case '-':
			flags |= LEFT;
			goto repeat;
		case '+':
			flags |= PLUS;
			goto repeat;
		case ' ':
			flags |= SPACE;
			goto repeat;
		case '#':
			flags |= SPECIAL;
			goto repeat;
		case '0':
			flags |= ZEROPAD;
			goto repeat;
		}
		field_width = -1;
		if (is_digit(*fmt)) //如果为数字，则直接取数字，如果为*则取下个参数值
			field_width = skip_atoi(&fmt);
		else if (*fmt == '*') {
			field_width = va_arg(args, int);
			if (field_width < 0) {
				field_width = -field_width;
				flags |= LEFT;
			}
		}

		/* get the precision */
		precision = -1;
		if (*fmt == '.') {
			++fmt;
			if (is_digit(*fmt))
				precision = skip_atoi(&fmt);
			else if (*fmt == '*') {
				/* it's the next argument */
				precision = va_arg(args, int);
			}
			if (precision < 0)
				precision = 0;
		}

		/* get the conversion qualifier */
		qualifier = -1;
		if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') {
			qualifier = *fmt;
			++fmt;
		}

		switch (*fmt) {
		case 'c':
			if (!(flags & LEFT)) //不是左对齐，则在前面补空格，否则在后面补空格
				while (--field_width > 0)
					*str++ = ' ';
			*str++ = (unsigned char) va_arg(args, int);
			while (--field_width > 0)
				*str++ = ' ';
			break;

		case 's':
			s = va_arg(args, char *);
			len = strlen(s);
			if (precision < 0)
				precision = len;
			else if (len > precision)
				len = precision;

			if (!(flags & LEFT))
				while (len < field_width--)
					*str++ = ' ';
			for (i = 0; i < len; ++i)
				*str++ = *s++;
			while (len < field_width--)
				*str++ = ' ';
			break;

		case 'o':
			str = number(str, va_arg(args, unsigned long), 8, field_width,
					precision, flags);
			break;
		case 'p': //指针类型
			if (field_width == -1) {
				field_width = 8;
				flags |= ZEROPAD;
			}
			str = number(str, (unsigned long) va_arg(args, void *), 16,
					field_width, precision, flags);
			break;
		case 'x': //16进制
			flags |= SMALL;
		case 'X':
			str = number(str, va_arg(args, unsigned long), 16, field_width,
					precision, flags);
			break;
		case 'd': //整数
		case 'i': //有符号
			flags |= SIGN;
		case 'u': //无符号
			str = number(str, va_arg(args, unsigned long), 10, field_width,
					precision, flags);
			break;
		case 'n': //停止打印，并将已经打印的字符数写入到int指针指向的地址
			ip = va_arg(args, int *);
			*ip = (str - buf);
			break;
		default:
			if (*fmt != '%')
				*str++ = '%';
			if (*fmt)
				*str++ = *fmt;
			else
				--fmt;
			break;
		}

	}
	*str = '\0';
	return str - buf;
}
